Tetragonal rare earth (R) Iron borides, R 1+εFe 4B 4 (ε≅0.1), with incommensurate rare earth and iron substructures

Abstract

Crystallographic and magnetic properties of a new structural series of ternary borides with composition R 1+εFe 4B 4 (R = Ce, Pr, Nd, Sm, Gd, Tb, 0.11(Pr) ≤ε≤ 0.15(Tb) are reported. The compounds are built of incommensurate substructures of rare earth atoms (linear strings ⧸⧸ c̄), iron atoms (chains of edge sharing tetrahedra ⧸⧸ c̄),and boron atom pairs. A single crystal X-ray diffraction study of one representative (Sm 1.13Fe 4B 4) based on a commensurate structure model (composition : Sm 17(Fe 4B 4) 15, a = 7.07 Å, c ≡ 17c Sm ≡ 15c Fe= 58.69 Å, space group P4 2/n) revealed a periodic twist modulation of the Fe tetrahedra chains around c̄. Magnetic susceptibility measurements on single crystals of another representative (Nd 1.11Fe 4B 4) revealed ferromagnetic ordering at T c = 13 K. Above this temperature the magnetic properties are dominated by ferromagnetic inclusions (Fe 2B, Nd 2Fe 14B).